The aim of the proposed research is to understand how ethanol affects the function of muscarinic acetylcholine receptor complexes in the brain. We have demonstrated that ethanol 1) alters ligand binding to the receptor and 2) disrupts receptor coupling to guanine nucleotide-dependent transducer proteins (G proteins). The latter effect represents a novel mechanism for disruption of synaptic transmission. The hypotheses to be tested are that ethanol interacts with muscarinic-G protein complexes in the brain, thereby affecting 1) ligand binding to the receptor, 2) gaunine nucleotide regulation of receptor binding, 3) receptor regulation of postsynaptic biochemical events, 4) guanine nucleotide binding to receptor-associated G proteins, and/or 5) the GTPase activity of G proteins. Accordingly, the Specific Aims of the proposed research are to determine the effects of ethanol and other short cahin alcohols on muscarinic (and other) receptors and their associated G proteins in rat brain. Receptor processes to be studied are 1) ligand binding, including antagonist binding site density, affinity, kinetics and thermodynamics, and agonist binding propetties (subpopulation distribution and affinities), 2) receptor-G protein coupling, as revealed by guanine nucleotide regulation of agonist binding, 3) muscarinic receptor-mediated inhibition of adenylate cyclase activity and stimulation of phosphatidylinositol breakdown in brain membranes, as an indication functional muscarinic transmission, and 4) the GTPase and (345)GTP binding activities of G protein species isolated from rat brain, to evaluate the possibility of direct alcohol-G protein interactions. This research will increase our understanding of muscarinic receptor organization and function in the brain and provide insight into the molecular bases for ethanol disruption of synaptic transmission.